How to select into multiple variables inside a trigger function? - postgresql

Question

This is what I'd like to achieve:
CREATE FUNCTION f() RETURNS trigger AS $$
BEGIN
SELECT COUNT(*) AS total_num, SUM(width) AS total_width
FROM some_table WHERE foo = NEW.foo;
IF total_num > 0 AND total_width > 100
THEN
RAISE EXCEPTION 'this is bad';
END IF;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
But it's not yet syntactically correct.
I've read I first need to DECLARE the variables (in this case total_num and total_width) so I can use those and use SELECT INTO but I've seen examples with a single variable / SELECT statement only. What if I have more of them?

Answer 1

You can list multiple variables in the into part. And the declare section needs to come before the first begin:
CREATE FUNCTION f() RETURNS trigger
AS $$
declare
total_num bigint;
total_width bigint;
BEGIN
SELECT COUNT(*), SUM(width)
into total_num, total_width
FROM some_table
WHERE foo = NEW.foo;
IF total_num > 0 AND total_width > 100 THEN
RAISE EXCEPTION 'this is bad';
END IF;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;

Answer 2

Edit: I'm not sure whether the emphasis here is on the use of variables or the actual IF. This is meant as an answer on the latter:
You can do this without variables using HAVING and EXISTS.
IF EXISTS (SELECT ''
FROM some_table
WHERE foo = new.foo
HAVING count(*) > 0
AND sum(width) > 100) THEN
RAISE EXCEPTION 'this is bad';
END IF;